1. Field of the Invention
The present invention relates to resilient support pads and, more particularly, to support pads made from a resilient material like foam rubber, including slots in the supporting surface thereof adapted for controlling surface strain thereof.
2. Description of the Prior Art
The use of slits or partitions to control the tensile characteristics of a foam rubber support pad have been known in the past. Most often such use is made when the phenomenon, often referred to as "the hammock phenomenon," is to be avoided.
Generally, the hammock phenomenon occurs as a result of the tensile stresses along the support surface of the pad which transforms the compressive load into a distributed tensile surface strain through shear transfers within the material of the pad. This hammock effect provides the often recognized undesirable result of reducing the support levels around a localized area of higher loading. Thus, two people lying on the same pad will often be directed towards each other with the uncomfortable associated result. To alleviate this problem in the past, slits, partly extending through the supporting surface of the pad, were formed, such slits providing a break in the tensile stress distribution to thereby localize any high pressure points. One example of such slitting is that shown in U.S. Pat. No. 3,512,190. Further improvements to this manner of spring control are shown in my prior U.S. Pat. No. 3,885,257. Both of the above-described techniques, and in particular the techniques described in my prior patent, are useful in controlling the strain propagation along the surface of the cushion or pad. My prior technique, in addition to control over strain propagation, also provides control over the compressive spring characteristics of the pads. The above-described techniques, while generally useful, have heretofore never been applied to the load distribution and strain distribution desired in a supporting surface of a mattress. In a mattress the support area immediately subjacent the upper torso of the supported person is most often exercised in transverse or lateral surface strain. Furthermore, this body area is relativelylarge and the resulting pressure thereof is therefore distributed over a substantially large surface. The lower torso, however, including the hip area of the person, both entails more localized pressure spots and additionally involves movements which are both longitudinal with the mattress and transverse or lateral across the mattress. This uneven loading of a mattress is often critical in medical applications where various incidents of trauma dictate various levels of control over the restraint and support levels achieved by the mattress.